List之Union(),Intersect(),Except() 亦可以说是数学中的并集，交集，差集

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Union()

这个方法将会Union(并集)两个序列(集合)连接成一个新列表(集合)

方法定义是:

public static IEnumerable<TSource> Union<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second)

public static IEnumerable<TSource> Union<TSource>(this IEnumerable<TSource> first,IEnumerable<TSource> second, IEqualityComparer<TSource> comparer)

Intersect ()

它将产生两个序列的交集.

方法定义是:

public static IEnumerable<TSource> Intersect<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second)

public static IEnumerable<TSource> Intersect<TSource>(this IEnumerable<TSource> first, Enumerable<TSource> second,IEqualityComparer<TSource> comparer)

Except ()

它是从一个集合中删除存在另一个集合中的项.两个序列产生的集合差. 英文意思是：除此之外

方法定义是:

public static IEnumerable<TSource> Except<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second)
public static IEnumerable<TSource> Except<TSource>(this IEnumerable<TSource> first, IEnumerable<TSource> second, IEqualityComparer<TSource> comparer)

实例代码分别如下：

using System;  
using System.Collections.Generic;  
using System.Linq;  
using System.Text;  
using System.Data;   
 
 
namespace test  
{  
    class Program  
    {  
        static void Main(string[] args)  
        {  
            IList<Student> oneStudents = new List<Student>();  
            oneStudents.Add(new Student(1,false,"小新1","徐汇"));  
            oneStudents.Add(new Student(2,false,"小新2","闵行"));  
            oneStudents.Add(new Student(3, false, "小新3", "嘉定"));  
            oneStudents.Add(new Student(4, false, "小新4", "闸北"));  
 
            IList<Student> twoStudents = new List<Student>();  
            twoStudents.Add(new Student(5, false, "小新5", "贵州"));  
            twoStudents.Add(new Student(6, false, "小新6", "湖北"));  
            twoStudents.Add(new Student(7, false, "小新7", "山东"));  
            twoStudents.Add(new Student(8, false, "小新8", "西藏"));  
 
            IList<Student> threeStudents = new List<Student>();  
            threeStudents.Add(new Student(1, false, "小新1", "徐汇"));  
            threeStudents.Add(new Student(2, false, "小新2", "闵行"));  
            var bingji = oneStudents.Union(twoStudents, new StudentListEquality()).ToList();//并（全）集   
              var jiaoji = oneStudents.Intersect(threeStudents, new StudentListEquality()).ToList();//交集   
              var chaji = oneStudents.Except(threeStudents, new StudentListEquality()).ToList();//差集  
 
              Console.WriteLine();  
            Console.WriteLine("以下是并集的结果");              
            bingji.ForEach(x =>  
            {  
                Console.WriteLine(x.StudentId.ToString() + "    " + x.Sex.ToString() + "   " + x.Name.ToString()+" "+x.Address.ToString());  
       
            });  
            Console.WriteLine();  
            Console.WriteLine("以下是交集的结果");             
            jiaoji.ForEach(x =>  
            {  
                Console.WriteLine(x.StudentId.ToString() + "    " + x.Sex.ToString() + "   " + x.Name.ToString() + " " + x.Address.ToString());  
 
            });  
 
            Console.WriteLine();  
            Console.WriteLine("以下是差集的结果");              
            chaji.ForEach(x =>  
            {  
                Console.WriteLine(x.StudentId.ToString() + "    " + x.Sex.ToString() + "   " + x.Name.ToString() + " " + x.Address.ToString());  
 
            });  
        }  
 
    }  
 
 
 
 
 
    public class Student  
    {  
        public Student(int studentId, bool sex, String name, String address)  
        {  
            this.StudentId = studentId;  
            this.Sex = sex;  
            this.Name = name;  
            this.Address = address;  
        }  
        public int StudentId { get; set; }  
        public bool Sex { get; set; }  
        public String Name { get; set; }  
        public String Address { get; set; }  
         
    }  
    public class StudentListEquality : IEqualityComparer<Student>  
    {  
        public bool Equals(Student x, Student y)  
        {  
            return x.StudentId == y.StudentId;  
        }  
 
        public int GetHashCode(Student obj)  
        {  
            if (obj == null)  
            {  
                return 0;  
            }  
            else 
            {  
                return obj.ToString().GetHashCode();  
            }  
        }  
    }  
 
 
 
}

以上运行的结果是：

以上的结果是重载了含有参数的IEqualityComparer<TSource> 方法，实现IEqualityComparer接口对数据进行了重复过滤，如果不实现这个方法结果是

var bingji = oneStudents.Union(twoStudents).ToList();//并（全）集
var jiaoji = oneStudents.Intersect(threeStudents).ToList();//交集
var chaji = oneStudents.Except(threeStudents).ToList();//差集

但是对于List<T>的T是简单类型，如int string long 。。。。。是怎么样的呢？代码如下所示

IList<int> firstNumbers = new List<int>()   
   
             {   
,2,3,4,5,6,7   
 
             };  
 
            IList<int> secondNumbers = new List<int>()   
   
             {   
,9,10   
 
             };  
 
            IList<int> thressNumbers = new List<int>()   
   
             {   
,2,3   
 
             };  
 
 
            var result1 = firstNumbers.Union(secondNumbers).ToList();  
            var result2 = firstNumbers.Intersect(thressNumbers).ToList();  
            var result3 = firstNumbers.Except(thressNumbers).ToList();  
            Console.WriteLine("以下是并集的结果");  
            result1.ForEach(x => Console.WriteLine(x));  
 
            Console.WriteLine();  
            Console.WriteLine("以下是交集的结果");  
            result2.ForEach(x => Console.WriteLine(x));  
 
            Console.WriteLine();  
            Console.WriteLine("以下是差集的结果");  
            result3.ForEach(x => Console.WriteLine(x));  
 
            Console.WriteLine("以上是简单类型如：int string long。。。。。没有实现IEqualityComparer<T>接口");

结果是：

说明一下刚回来看了下书，是差集不是补集、已更改！

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